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What am I doing wrong ??? Arduino - tachometer !? Answered

Hello ... I would like to ask, what am I doing wrong. I'm trying to create this instructable www.instructables.com/id/Arduino-Based-Optical-Tachometer/ ...

I downloaded the code, created the circuit (photo provided) ... and I'm using these components :
 1. IR LED = SFH487-3 www.maplin.co.uk/module.aspx (code CY88)
 2. Phototransistor = SFH300-3 www.maplin.co.uk/module.aspx (code NP64)
Resistors are the same value, like in the instructable.

Please, could you tell me, what am I doing wrong ???

Thank you very much.


P.S. : IR LED is working, the PhotoTransistor is working as well <- I tried to measure it with my voltmeter - for CONTINUITY ... and as I was getting closer to the IR light, the value was decreasing.

2 Replies

steveastroukBest Answer (author)2009-12-05

The headline circuit is wrong, very wrong. The phototransistor is wrong.

Put the 10K to +5v, then to the transistor collector, then tie the emitter to ground. Pick the signal for the arduino off from the collector. 


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zholy (author)steveastrouk2009-12-06

Thank you very much ... it's like you wrote. Now I remember, that I did the same with the LDR :( ...

Thank you.

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